The invention relates to photographic copying apparatus, and more particularly to improvements in photographic copying apparatus of the type wherein the light-transmitting opening between the original and the photosensitive image-receiving material is adjustable in dependency on the format of the original. Still more particularly, the invention relates to improvements in photographic copying apparatus wherein the original is imaged onto photosensitive material by a variable-focus optical system through the opening of a composite mask one or more sections of which can be shifted to change the size of the opening.
In presently known copying apparatus of the above outlined character, each change of format is followed by projection of the image of the original onto a circuit which is located in the plane of the photosensitive material. The attendant adjusts the variable-focus optical system until the size of the projected image on the screen matches the required dimensions. It is also known to calculate the necessary adjustment of the optical system for each desired size of the reproduction. Each of these procedures is time consuming and unreliable. In the first instance, inaccuracies are attributable to carelessness or lack of experience of the attendant and/or to fatigue (the attendant's eyes are likely to be tired after a relatively small number of adjustments). In the second instance, the calculated values are utilized to actuate the adjusting mechanism for the optical system. The accuracy of adjustment is limited, especially if the component parts of the mechanism are not machined and assembled with a high degree of precision. Furthermore, the number of possible adjustments of the optical system is very high. Thus, and assuming that the number of different formats is at least 27, that there are at least five different adjustments of the width of the exposed part of an original and at least four different widths of photographic paper, this would necessitate a total of 540 different adjustments of the variable-focus optical system.